The present invention relates to polymer photoresists with bound photoacid groups containing a urethane linkage, and methods of use, and more specifically, to polymers bearing pendant triarylsulfonium sulfonate groups for high resolution lithography.
The patterning of radiation sensitive polymeric films with high energy radiation flux such as photons, electrons, or ion beams is the principle means of defining high resolution circuitry found in semiconductor devices. The radiation sensitive films, often referred to as photoresists regardless of the radiation source, generally consist of multicomponent formulations that are coated onto a desired substrate such as a silicon wafer. The photoresist film is then exposed to a radiation. The radiation is most commonly ultraviolet light at wavelengths of 436, 365, 257, 248, 193 or 157 nanometers (nm), or a beam of electrons or ions, or soft x-ray radiation, also referred to as extreme ultraviolet (EUV) or x-rays. The radiation is exposed patternwise to induce a chemical transformation that renders the solubility of the exposed regions of the film different from that of the non-exposed areas. The film is then heated to enhance the radiation induced chemical transformation. After heating, the film is treated with an appropriate developer, usually a dilute, basic aqueous solution, such as aqueous tetraethylammonium hydroxide (TMAH) to develop the photoresist image on the wafer. Typical photoresist compositions generally comprise a polymer (which can be radiation sensitive or non-sensitive), a radiation sensitive component, a casting solvent, and optional performance enhancing additives. High performance photoresist compositions, in terms of sensitivity to radiation and resolution capability, are “chemically-amplified” photoresists. These photoresist compositions provide high resolution, high contrast, and high sensitivity that are not generally provided by other photoresists. Chemically amplified photoresists are based on a catalytic mechanism that allows a relatively large number of chemical events such as, for example, deprotection reactions in the case of positive-tone photoresists brought about by the application of a relatively low dose of radiation that induces formation of the catalyst, often a strong acid.
Most of the current positive-tone photoresist compositions comprise aqueous base soluble functional groups that are sufficiently protected with acid sensitive groups (e.g., esters capable of being cleaved by a strong acid to produce a carboxylic acid) such that the photoresist layer initially will not dissolve in an aqueous base developer. During exposure to radiation, a photoacid generator (PAG) present in the photoresist layer produces strong acid, which then catalyzes the removal of the acid sensitive groups on heating in a post-exposure bake (PEB). This process produces aqueous base soluble material in the exposed area, which is removed during development with a basic aqueous developer, thereby producing topographical patterned layers. Many of the current polymers used in photoresist compositions contain acid sensitive carboxylic ester groups, which are insoluble in aqueous base until the ester groups are deprotected by a photo-generated acid. The mechanism of the acid-catalyzed deprotection of the esters in the photoresist layer is shown in Scheme 1.

Water is not needed for the ester deprotection reaction to occur. However, chemically amplified photoresists, particularly in the sub-50 nm regime, experience diminished image resolution or contrast, often referred to as “image blur” (e.g., Hinsberg et al., Proc. SPIE, (2000), 3999, 148). Although chemically-amplified resists have been developed for 248, 193 and EUV lithography, barriers to achieving higher resolution and smaller feature sizes remain due to physical, processing and material limitations. Image blur is generally thought to result from two contributing thermally driven factors: gradient-driven acid diffusion and reaction propagation, the result being a distortion in the developable image (e.g., line pattern) compared to the projected aerial image transferred onto the film. The key metric controlling the image blur is the ratio R=(average rate of acid catalyzed deprotection)/(average rate of acid diffusion). The greater the value of the ratio R is, the lower the image blur (Hinsberg et al., Proc. SPIE, (2004), 5376, 21).
One approach to improving line resolution is to incorporate the photo acid generator (PAG) into the polymer structure rather than using it as a small molecule additive. Japanese publication JP2006178317 to Hatakeyama et al. describes a large number of PAG-containing monomers that can be incorporated into a PAG polymer. Despite the improvements in resolution with these materials, existing PAG polymers are generally limited to a 28 nm line/space patterns.
Therefore, ongoing needs exist for photoresist compositions having improved image resolution capability and improved methods of patterning substrates.